[Shop-talk] Jump starting a late model car

[Donald H Locker]

I think someone is pulling someone else's leg. There is nothing (that I know of) in any post-2000 vehicle that can be "fried" by providing or accepting a jump, provide it's done properly (+ to + and - to -).

The "dead" battery does not appear as a short because the cables and clamps have significant resistance. That is the big reason that the "dead" battery needs to be connected for a period of time before cranking. (I usually wait 30 sec (longer in winter); not very long, but it really doesn't take much to bring a dead battery up to sufficient charge.)

The protections on vehicle electronics and electrical systems are amazing; I've helped design and test quite a few of them. Protection is built in to every component against: over-voltage; reverse connection; shorts to ground; shorts to power. The battery itself is a very simple electrochemical device that _can_ be damaged, but it's difficult: freezing (-40F if charged; -20F if significantly discharged); reverse charging; mechanical damage is the most common problem.

Provided the jumper and jumpee batteries are connect properly (+ to + and - to -), there is almost no way to damage either of the vehicles' systems.

Donald.

On 2023-11-30 17:12, JohnT Blair wrote:

> I come to the well of knowledge looking for information.
>
> My sister just emailed me about her having a friend jump start her late model Lexis from his F150 pickup. He got her started and then drove his truck to someplace and parked it. When he tried to start it, it wouldn't start. He had it towed to a dealership and they said his battery was fried.
>
> In my sister's email she said that she has found out that you shouldn't jump start a car made from 2000 on.
>
> My question is why and how do you start a car with a dead battery?
>
> I realize that the jumping car should be running, so that gives the possiblity of too much current being drawn from the jumping car as it's got a good battery and an alternator capable of putting out well over 100A! So the jumped car's dead battery looks like a short circuit. Bad - lots of current!
>
> So disconnecting the dead battery and putting it on a battery charger to give it a more controlled charge should be OK.
> But that's not easy to do in a parking lot.
>
> What about these jump boxes, especially the little ones like
>
> https://www.walmart.com/ip/NEXPOW-Battery-Jump-Starter-1500A-Peak-12800mAh-Car-Starter-up-7-0L-Gas-5-5L-Diesel-Engine-12V-Portable-Booster-Power-Bank-Box-LED-Light/534414164?adsRedirect=true
>
> But that is supposedly capable of 1500A!!!
>
> I did a google search on the subject and found an article talking about all the problems that you can have doing this. But the article really didn't say if these problems were to the jumping or the jumped car or both.
>
> So what is the collective knowledge about this? What am I missing?
>
> JohnT,
>
> John T. Blair WA4OHZ email: jblair1948 at cox.net
>
> Va. Beach, Va Phone: (757) 495-8229
>
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>
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>
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